Little is understood about what factors might explain why Black women tend to be diagnosed with more aggressive disease than White women. Based on characterization by immunohistochemical (IHC) markers, in every age group, White women have the highest rates of estrogen receptor (ER)+ breast cancer and Black women have the highest rates of ER- breast cancer. Moreover, triple negative breast cancer [TNBC; ER-, progesterone receptor (PR)-, human epidermal growth factor receptor 2 (HER2)-], an aggressive subset of basal-like breast cancer, is more common among Black women than among White women and has a worse prognosis than other subtypes. Recent studies, conducted largely among White women, have reported differences in risk by breast cancer subtype associated with hormone-related and other risk factors, such as age at menarche, oral contraceptive use, parity, age at first full-term birth, breastfeeding, age at menopause, hormone replacement therapy use, obesity and physical activity, suggesting that subtypes of breast tumors may have distinct etiologies. Few breast cancer studies have included large numbers of Black women, despite known marked racial differences in cancer incidence by subtype, and most studies did not collect tumor tissue to allow for detailed characterization of tumor subtypes. To address this issue, we propose to collect tumor tissue specimens from 710 Black breast cancer cases, to classify breast tumors by hormone-receptor status, and to examine associations between hormone-related and other risk factors and breast cancer subtypes among Black women. The association of breast cancer with many modifiable risk factors appears to differ by tumor subtype; therefore, it is essential to perform subtyping of all breast tumors in future studies. The utilization of a soon to be completed population-based case-control study of Black women is a highly efficient approach to the collection and classification of breast cancer tumor tissue since we have already obtained participants' permission. This proposed project will be one of the most comprehensive and well-powered studies to investigate the associations between hormone-related and other risk factors and breast cancer subtypes among Black women. Moreover, the collection of tumor tissue will provide immediate future opportunities to extend these risk factor analyses to intrinsic molecular subtypes. The results of this study will fill an important gap in current knowledge regarding assessment of hormone-related factors that increase risk for aggressive breast cancer among Black women, and will assist in delineating Black women at high (or low) risk for breast cancer subtypes with a poor prognosis who will most benefit from screening, and may provide new targets to reduce the risk of aggressive breast cancer among Black women. This may pave the way for the development of clinically useful breast cancer prediction models specific to race and breast cancer subtype.